I'm not sure there is such a thing as surefire talent other than at the very top of a draft -- and maybe not even then. Lots of first-round rookies need to be eased into a starting role. Peppers will be a day one contributor at least on special teams, and probably pretty significant.
Hooker has injury concerns, and while "can't tackle" is clearly hyperbole, saying that tackling is a weakness probably isn't. And given the historic problems we've had stopping the run, I can certainly see preferring a plus tackler as a safety to a minus one.
I was not initially a fan of drafting the guy -- based basically on listening to what folks here were saying --, but since seeing that video and reading up on Williams' defense, it's a pick that makes sense to me.
Plus, it is apparent the Browns determined that there was not a QB available to us around 12 who fit the "franchise" need. That automatically puts us in the franchise QB sweepstakes for next year, so accumulating an additional first round pick as ammo is almost a no brainer.